The present invention relates to a magnetic disc drive apparatus having a read/write head and an erase head and in particular to a magnetic flexible disc drive apparatus in which unwanted influence on the read/write head due to leakage magnetic flux from the erase head is reduced.
FIG. 1 shows a first prior art tunnel erase type magnetic head in a flexible disc drive apparatus.
A read/write head 1 comprises a core assembly including a pair of cores 3 opposing each other with a read/write head gap 2, a bridging bar 5 which bridges both cores 3 and 3 to form a magnetic path and a read/write coil 6 wound on one of the cores 3. The coil 6 is adapted to be energized with a write current IW.
The erase head 7 is spaced from the read/write head 1 by a distance of d1. The erase head 7 comprises a pair of core assemblies 8 opposing each other with a space equal to the width of the core 3 so that the center axis between the cores 8 is aligned with the cores 3 and an erase coil 9 wound on the core assembly 8. The erase coil is adapted to be energized with a d.c. current Ie to build a d.c. magnetic field. Each core assembly 8 includes a bridge bar 12 which bridges both cores 11 opposing each other with an erase gap 10.
In the first prior art magnetic disc drive apparatus which is constructed in such a manner, data is stored on the magnetic disc 24 by the read/write head 1 to form a data stored track AW by rotating the magnetic disc in a direction as shown by an arrow A in FIG. 2. The magnetic disc at both sides of the data stored track A is erased by the erase head 7 to form erased tracks Ae. This prevents the read data from deteriorating due to cross talk of previous data even if the position of the read/write head 1 is slightly shifted radially when the stored data is read out.
FIG. 3 shows a second prior art magnetic head in a disc drive apparatus. This magnetic head is characterized in that its formation is simplified by forming an integral erase head 7. This magnetic head in a disc drive apparatus is operated in the same manner as the first prior art apparatus.
In the first and second prior art apparatus, when one block data unit, which is called a sector, is written along one track on the magnetic disc shown radially in FIG. 2, simultaneous conduction of the write current IW and the erase current Ie causes shifts between the written data track zone AW and the erase track zones Ae, Ae because of distance d2 between the read/write head gap 2 and the erase gap 10. Accordingly time delays De1 and De2 are usually provided for the erase current Ie at the beginning and the end of the write operation respectively, as shown in FIG. 4, so that the stored data track AW is sandwiched between the erase track zones Ae, Ae at the both sides
Since transition of magnetic field due to turning off of the erase current Ie at the end of the erase delay time De2 induces the generation of noise voltage in the R/W coil 6 on the read/write head 1, it makes it difficult to read the subsequent sector for the interval of the erase delay time De2. Accordingly it is necessary to provide a space at least equal to the length d2 between the adjacent sectors. The length d2 should be as short as possible to efficiently use tracks on the magnetic disc 24. The common integration of the core 3 of the read/write head 1 and the core 11 of the erase head 7 in the third prior art apparatus, as shown in FIG. 5, has been proposed in order to provide a decreased length d2.
Decreasing the length d2 however involves disadvantages in that the fabrication of cores is difficult due to small size of core as well as the fact that the d.c. magnetic field of the erase head 7 is readily coupled with the read/write head to provide the recorded wave form on the disc with asymmetry. The term asymmetry means the difference in the length of magnetized region on the magnetic disc, even if a write current which is positively and negatively symmetrical is applied. This lowers the read margin of the data since the peak position is shifted on reading.
The length d2 is usually in the order of 0.9 mm. The increase in ampere turn of the erase coil 9 for the enhancement of the erasure efficiency of the erase head under such length d2 may involve the same disadvantages.